A conventional vehicle-mounted navigation device displays the current position of a vehicle on a digital map (simply referred to as a “map” from here on) displayed on a display unit while superimposing the current position on the map. Furthermore, the conventional vehicle-mounted navigation device searches for a route leading from the current position of the vehicle to a destination, and displays the recommended route on the map. In addition, the conventional vehicle-mounted navigation device carries out route guidance of the recommended route on the basis of map information read from a recording medium.
By the way, a car pool lane (Car Pool Lane) or the like which is used in a road system mainly seen in, for example, a North American big city is known as a road on which restrictions showing which vehicles can enter the road are imposed. A car pool lane is also called an HOV lane and is a lane along which only vehicles with two or more people are allowed to travel. A special lane disposed along with lanes on a freeway, a lane which is a shortcut of an interchange, etc. are known as car pool lanes. A road system which adopts such a car pool lane provides users with a preferential treatment that makes it possible to arrive at the destination in a shorter time as long as they travel along a carpool lane so as to prod users to share a vehicle with one or more persons, thereby reducing the traffic as a whole and therefore reducing traffic congestions.
As a technology related to such a car pool lane, patent reference 1 discloses a navigation device that enables a vehicle to efficiently travel along a lane on which restrictions showing which vehicles can enter the lane from another lane and exit the lane into another lane are imposed. This navigation device reads map data including road information about entering and exiting points in each highway equipped with a car pool lane from a DVD, and stores the map data in a data buffer. A route search processing unit performs a route searching process in consideration of whether or not car pool lanes can be used by using the map data stored in the data buffer. When performing a route guidance using carpool lanes, a carpool lane guidance unit performs a predetermined lane change guidance using an image and voice at a time when each of the entering and exiting points at which the vehicle should change its travelling direction gets close to a point at a predetermined distance or less from the position of the vehicle.